Preparation of liquid alkylated pentaborane-9



United States atentO PREPARATION OF LIQUID ALKYLATED PENTABORANE-9 George E. Ryschkewitsch, Columbus, Ohio, assignor, by

mesne assignments, to Olin Mathieson Chemical Corporation, a corporation of Virginia No Drawing. Filed Dec. 1, 1955, Ser. No. 550,302

10 Claims. (Cl. 260-6065) I My invention relates to the manufacture of alkylated pentaboranes and, in particular, to the alkylation of pentaborane-9 with monoolefin hydrocarbons while the reactants are in admixture with tetrahydroturan, a lower monoalkylated tetrahydrofuran or a mixture thereof. The products produced in accordance with the method of my invention can be used as fuels when burned with air, as described in the application of Chiras and Mezey, Serial No. 501,742, filed April 15, 1955.

It isknown in the art to prepare pentaborane, which is a relatively stable, colorless liquid melting at --46.8 C. Pentaborane is a boron hydride or borane, and the art is aware that the burning of a borane with oxygen liberates considerably more energy than the oxidation of a corresponding amount of hydrocarbon, producing very high flame temperatures. This suggests the use of pentaborane as a fuel of very high energy content. Pentaborane sufiers from the disadvantage, among other things, however, that it has a relatively high vapor pressure, its vapor pressure being 66 mm. of mercury at C. and its boiling point at atmospheric pressure being 58 C.

One of the objects of my invention is to provide a method for producing liquid alkylated pentaboranes which are less volatile and less toxic than pentaborane-9 but at the same time approaching pentaborane-9 insofar as heat of combustion is concerned. Thus, in accordance with my invention, I have discovered that pentaborane-9 can be reacted with monoolefin hydrocarbons containing from 2 to 5 carbon atoms while in admixture with tetrahydrofuran, lower monoalkylated tetrahydrofurans or mixtures thereof to provide alkylated pentaboranes which are stable, relatively non-volatile liquids with convenient handling characteristics. By this process, monoolefin hydrocarbons which are available at rather low cost and large tonnages can be reacted with pentaborane-9 to form valuable alkylated pentaboranes in yields which are substantially greater than those which are obtained when the olefins and pentaborane are reacted not in admixture with the tetrahydrofuran or alkylated tetrahydrofuran.

The exact manner of the action of tetrahydrofuran or alkylated tetrahydrofuran in increasing the yield of the alkylation reaction is not known to me. Thus, they may be acting as a solvent or as a solvent and catalyst. It has been shown, however, that substantial increases in the yield of alkylated products can be obtained when pentaborane-9 is alkylated with the olefin in the presence of the tetrahydrofuran or alkylated tetrahydrofuran, in comparison with the yield obtained when the pentaborane-9 is alkylated with the olefin but without tetrahydrofuran or alkylated tetrahydrofuran.

The following example illustrates an embodiment falling within the scope of my invention and is to be considered not limitative. In the example, the term millimoles signifies milligram moles.

Example this experiment 10.00 millimoles of pentaborane-9 ensed into a 60 ml. glass bulb which was im- 2,983,760 Patented May 9, 196 1- ice mersed in a Dewar flask filled with liquid nitrogen (temperature -196 0.). Then 10.7 millimoles of tetrahydrofuran, followed by 9.92 millimoles of isobutene, were condensed in the bulb at the same temperature. At this temperature the reactants were solids. The bulb was sealed, removed from the cooling flask, allowed to warm to room temperature and then heated for 7 /2 hours at C. in a Fisher Isotemp oven. After being removed from the oven the bulb was allowed to cool to room temperature and then attached to a vacuum line. In the next step it was cooled with liquid nitrogen and opened to the vacuum line. i

A part of the crude product in the bulb-was allowed to warm up and was fractionated through a series of cold traps. In the first instance the material was allowed to pass through three traps, the first being held at 78 C., the second at 116 C., and the third at 196 C. Through a series of additional fractionation operations, carried out with cold traps, unreacted pentaborane-9 and the tetrahydrofuran were finally isolated in a 78 C. trap and the hydrocarbon fraction in a 196" C. trap. Assuming that the tetrahydrofuran was not used up during the reaction, the quantity of pentaborane-9 in the trap was determined by the difference. The hydrocarbon fraction was analyzed for olefin by conventional gas analysis, and was found to contain 0.37 millimole of isobutane and 1.41 millimoles of isobutene.

The remaining material :in the bulb was fractionated through a series of four cold traps held at -8 C., -18 C., 52 C. and 78 C., respectively. In the trap held tit-52 C. a fraction was obtained which exhibited a vapor pressure of 4.4 mm. at 26.5 C. temperature. This material was refractionated through three traps held at -8 C., 18" C., and -52l C., respectively, and in the 52 C. trap there was collected a product which had a vapor pressure of 5 mm. at 24 0.; this vapor pressure corresponds closely with the vapor pressure of ter-butylpentaborane. The weight of isobutylpentaborane was 60.7 percent based on the pentaborane used in the reaction. Some of the pentaborane-9 consumed was transformed into tri-iso-butylborane and other viscous liquids containing carbon which are not volatile at room temperature. The amount of tri-isobutylborane formed in the reaction was 1.18 millimoles.

A controlled run in which tetrahydrofuran was not present was also completed, anda comparison of the results obtained in this run with the run in which tetrahydrofuran was present is given in Table I below:

1 B5119 was recovered in a mixture with tetrahydrotuiran. B 119 consumption calculated by assuming no change in the amount of tetrahydrofuran had occurred during the reaction.

Various modifications can be made in the procedures of the specific example to provide other embodiments which fall within the scope of my invention. Thus, in place of the isobutylene utilized, there can be substituted other monoolefin hydrocarbons having from 2 to 5 carbon atoms, for example, ethylene, propylene, l-butene, Z-butene and the like, as well as mixtures thereof; Also in place of the tetrahydrofuran there can be substituted other lower monoalkylated tetrahydrofurans, particularly thosev not eontaining more than four carbon atoms, in the allgylj-radical', for example, 2,-methyl-tetrahydrofuran, 2- ethyl-tetrahydrofuran and the like, as Well as mixtures thereof;

In general, the reaction temperature employed will be within the range from about 130 C. to about 190 0., although somewhat higher aswell as somewhat lower reaction temperatures can be used. In like manner, the reaction time can be varied widely, generally being within the range from about 1 to about 24 hours and preferably within the range from about 4 to about 8 hours. The ratio of olefin to pentaborane-9 utilized in carrying out my process can be varied Widely, generally being within the range from 0.1 to 10 moles of olefin per mole of pentaborane-9,. The preferred range of olefin to pentaborane-9 employed is from 0.5 to 2.0 moles-of olefin to 1 mole of-pentaborane-9, dependingupon the degree of alkylation desired; The quantity of tetrahydrofuran or monoalkylated tetrahydrofuran used will generally vary from about 1 to moles per mole of pentaborane-9.

I claim:

1. A method for the preparation of a liquid reaction productofjpentaborane-9 and a monoolefin hydrocarbon having from 2 to 5, carbon atoms which comprises reacting from 0.1 to moles ofthe monoolefin hydrocarbon per mole of the pentaborane -9 at a temperature within the range from 130 to 190 C, while the reactants are in admixture with from 1, to 5 moles, per mole of pentaborane-9, of at least one material selected from the group :5. consisting of tetrahydrofuran and lower mcnoalkylated tetrahydrofurans.

2. The method of claiml wherein said monoolefin hydrocarbon is ethylene.

3. The method of claim hydrocarbon is isobutylenea 4. The method of claim hydrocarbon is propylene.

5. The method of claim tetrahydrofuran.

6. A method for the preparation of a liquid reaction product of pentaborane-9 and a monoolefin hydrocarbon having from 2 to 5 carbon atoms which comprises reacting from 0.5 to 2 moles of said monoolefin hydrocarbon per one mole of pentaborane-9 at a temperature within the range from to C. while the reactants are in admixture with from 1 to 5 moles, per mole of pentaborane-9, of at least one material selected from the group consisting, of tetrahydrof uran' and lower" monoalkylated'tetrahydrofurans..

7. The method of claim 6" wherein said monoolefin hydrocarbon is ethylene. V

8. The method of claim 6 wherein said monoolefin hydrocarbon is isob utylene 9; The method of claim 6' wherein. said monoolefin hydrocarbon is propylene.

10. The method of claim 6'wl1erein said material is tetrahydrofuran.

1 wherein said monoolefin 1 wherein said monoolefin 1' wherein said material is References-Cited in the file of this-patent Hurd: J. Amer. Chem. Soc., 70, pages 2053-55 (1948). (Copy in Patent Ofiice Library.) 

1. A METHOD FOR THE PREPARATION OF A LIQUID REACTION PRODUCT OF PENTABORANE-9 AND A MONOOLEFIN HYDROCARBON HAVING FROM 2 TO 5 CARBON ATOMS WHICH COMPRISES REACTING FROM 0.1 TO 10 MOLES OF THE MONOOLEFIN HYDROCARBON PER MOLE OF THE PENTABORANE-9 AT A TEMPERATURE WITHIN THE RANGE FROM 130* TO 190*C. WHILE THE REACTANTS ARE IN ADMIXTURE WITH FROM 1 TO 5 MOLES, PER MOLE OF PENTABORANE-9, OF AT LEAST ONE MATERIAL SELECTED FROM THE GROUP CONSISTING OF TETRAHYDROFURAN AND LOWER MONOALKYLATED TETRAHYDROFURANS. 